7bf5769658
Some doorhangers are anchored to the Extensions Button via PopupNotifications.show() + gUnifiedExtensions.getPopupAnchorID(). The default behavior of PopupNotifications is to fall back to a different anchor if the specified anchor is invisible. But if the Extensions Button is hidden, we want to show it as needed, instead of triggering the fallback. This patch reveals the Extensions Button when PopupNotifications is about to show the panel. This button will automatically be hidden when the doorhanger is closed, as verified by the tests. Differential Revision: https://phabricator.services.mozilla.com/D248163